1. Field of the Invention
The present invention relates generally to a high frequency oscillator, and more particularly to an arrangement for stabilizing the oscillation frequency and phase of a high frequency oscillator for use in a microwave data communication device or the like.
2. Description of the Prior Art
A high frequency oscillator for use in a microwave data communication device requires a highly stable oscillation frequency and phase against microphonic vibrations, which would exert bad influence thereon.
FIGS. 1 and 2 depict a conventional arrangement for stabilization of the oscillation frequency and phase of a high frequency oscillator accommodated in a shielding case 1 of aluminum formed by die casting.
The high frequency oscillator comprises a printed circuit board 4 secured to the shielding case 1 by means of a plurality of screws 2 and an oscillator component 7 mounted on an area 3 formed on the printed circuit board 4. The oscillation frequency is determined by a circuit constant of the oscillator and a space defined by the shielding case 1 and a cover 8.
FIGS. 3 and 4 depict another conventional arrangement for stabilization of the oscillation frequency and phase of a high frequency oscillator.
The high frequency oscillator of FIGS. 3 and 4 is a packaged oscillator 9 in which an oscillation circuit is mounted in a shielded package and which is mounted on a printed circuit board 4 secured to a shielding case 1 by means of a plurality of screws 2. In this oscillator, the oscillation frequency depends on the packaged oscillator itself.
In an oscillator utilized in a microwave data communication device or the like, because a modulated carrier is further digitally modulated, the frequency and phase of the oscillator must be highly stable against microphonic vibrations. To satisfy this characteristic, the oscillator of FIG. 1 employs a cover 8 of aluminum formed by die casting, which makes substantially unchanged space conditions determined by the shielding case 1 and the cover 8 against the microphonic vibrations. In the oscillator of FIG. 3, the use of the packaged oscillator 9 makes space conditions in the package substantially unchanged even if those determined by the shielding case 1 and the cover 8 change. Accordingly, the frequency and phase of the oscillator are stable against microphonic vibrations.
In the case of FIG. 1, however, because the cover 8 is required to have the same size as that of the shielding case 1, vibrations occasionally cause distortion particularly in the proximity of the center of the cover 8. Accordingly, the cover 8 must be made thick and strong, for example, by aluminum die casting, and therefore, the oscillator becomes expensive and cannot be made compact.
In the case of FIG. 3, the packaged oscillator 9 itself is very expensive. Furthermore, because the oscillator 9 requires a wide area on which it is mounted, it cannot be made compact.